1. Technology Field
The present invention relates to a turbine system adapted for starting-controlling a turbine having a casing and a turbine rotor rotatably attached into the casing, and also relates to a method for starting-controlling the turbine system. In particular, this invention relates to the turbine system adapted for starting the turbine, while controlling thermal stress generated in the turbine rotor as well as controlling an expansion difference, due to thermal expansion, between the casing and the turbine rotor, and also relates to the method for starting-controlling the turbine system.
2. Background Art
Generally, when the turbine is started, temperature of steam discharging into the casing of the turbine is elevated, while a flow rate of the steam is increased, so that the surface temperature of a metallic material located on the surface of the turbine rotor is first elevated. Then the heat of the surface of the turbine rotor is transmitted to the interior of the turbine rotor by heat conduction. Therefore, the internal temperature of the metallic material located in the turbine rotor is elevated later than the surface temperature of the metallic material on the surface of the turbine rotor. As a result, a difference of temperature distribution occurs between the surface and the interior of the turbine rotor, leading to thermal stress exerted on the turbine rotor. If such thermal stress is considerably great, the life span of the turbine rotor may be substantially shortened.
To address this problem, a system for controlling start of the turbine, such that the thermal stress generated in the turbine rotor of the turbine can be controlled to be lower than a defined value as well as the time required for starting the turbine can be made shorter, has been known (e.g., see Patent Documents 1 and 2).
In the system for starting-controlling the steam turbine described in the Patent Document 1, the start of the turbine is controlled, by obtaining a turbine-speed increasing ratio indicative of a ratio of changing the rotating speed of the turbine rotor and a load increasing ratio indicative of a ratio of increasing load of a power generator, such that the temperature of a first-stage metal located at a first stage on an outer circumference of the turbine rotor, or the like, can be changed in accordance with a predetermined changing pattern.
Meanwhile, the system for starting-controlling the turbine described in the Patent Document 2 is configured for performing calculation on the assumption that both of the turbine-speed increasing ratio of the turbine rotor and the load increasing ratio of the power generator are constant, thereby to substantially reduce the number of variables used in the calculation, thus facilitating the calculation.
Patent Document 1: JP9-317404A
Patent Document 2: JP2006-257925A
However, when the turbine is started, the temperature of the steam passing through a steam passage provided between the turbine rotor and the casing storing the turbine rotor therein is raised, and the flow rate of the steam increases. In this case, both of the turbine rotor and casing are expanded in a longitudinal direction of the turbine rotor. However, the material and the shape of the turbine rotor are different from the material and the shape of the casing respectively. Accordingly, an amount of expansion of the turbine rotor is different from the amount of expansion of the casing, and a tendency in change of the amount of expansion of the turbine rotor is different from the tendency in change of the amount of expansion of the casing. Therefore, an expansion difference, which is a difference in expansion between the turbine rotor and the casing, may be seriously great. In the worst case, a rotatable member provided to the turbine rotor may be in contact with a stationary member provided to of the casing.